Discourse deficits following right hemisphere damage in deaf signers

Previous findings have demonstrated that hemispheric organization in deaf u sers of American Sign Language (ASL) parallels that of the hearing populati on, with the left hemisphere showing dominance for grammatical linguistic f unctions and the right hemisphere showing specialization for non-linguistic spatial functions. The present study addresses two further questions: firs t, do extra-grammatical discourse functions in deaf signers show the same r ight-hemisphere dominance observed for discourse functions in hearing subje cts; and second, do discourse functions in ASL that employ spatial relation s depend upon more general intact spatial cognitive abilities? We report fi ndings from two right-hemisphere damaged deaf signers, both of whom show di sruption of discourse functions in absence of any disruption of grammatical functions. The exact nature of the disruption differs for the two subjects , however. Subject AR shows difficulty in maintaining topical coherence, wh ile SJ shows difficulty in employing spatial discourse devices. Further, th e two subjects are equally impaired on non-linguistic spatial tasks, indica ting that spared spatial discourse functions can occur even when more gener al spatial cognition is disrupted. We conclude that, as in the hearing popu lation, discourse functions involve the right hemisphere; that distinct dis course functions can be dissociated from one another in ASL; and that brain organization for linguistic spatial devices is driven by its functional ro le in language processing, rather than by its surface, spatial characterist ics. (C) 1999 Academic Press.